Electric discharge apparatus



E. F. LOWRY ELECTRIC DISCHARGE APPARATUS Nov. 23, 1937.

Filed Oct. 3, 1935 2 She ets-Sheet l Insulafia INVENTOR Erwin F Lowr WITNESSES:

Patented Nov. 23, 1937 PATENT orrlcs ELECTRIC DISCHARGE APPARATUS Erwin F. Lowry, Forest Hills, Wilkinsburg, Pa.

assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa a corporatlon of Pennsylvania Application October 3, 1935, Serial No. 43,347

6 Claims.

My invention relates to electric discharge apparatus and it has particular relation to hot cathode discharge apparatus in which the electrodes operate in an atmosphere of gas or vapor.

A hot-cathode gas-filled discharge device is. in general, provided with a cathode consisting of a suitable base, preferably an alloy comprised of nickel, cobalt and ferrotitanium, coated with an emissive material, preferably a mixture of alkaline-earth oxides. When such an element is heated, electrons are emitted by the coating. In addition to the emissive electrode, an anode is provided. A difference of potential is impressed between the anode and the cathode and current 15 is transmitted between these electrodes.

In a gaseous discharge device, the electrons emitted by thecathode react on the gaseous or vapor medium in which the electrodes are immersed to produce positive ions which drift towards the cathode under the action of the electromotive force impressed between the cathode and anode. When the cathode is heated to the proper temperature, sufficient electrons are emitted from its surface to protect the coating from 25 the efiects of the positive ions which are drawn to the cathode. If, however, the cathode is not heated to a suificiently high temperature at the same time a potential difference is impressed between the anode and the cathode, the positive 30 ions impinging on the cathode attack the emissive coating. In addition the are which is produced under the action of the anode-cathode potential has a comparatively high potential drop by reason of the scarcity of electrons emit- 35 ted from the cathode. Under such circumstances hot spots tend to form on the surface of the cathode with the result that considerable portions of the active coating are stripped.

Customarily, the discharge devices of the type involved here are provided with cathodes which must be heated for a considerable interval of time before they are safe from positive ion bombardment. As the current output for which the discharge device is provided increases, the size of the cathode increases and the time required for heating the cathode to the proper temperature correspondingly increases. The necessary time may vary from five seconds to approximately 5 minutes or more.

50 It is an object of my invention to provide a discharge device of the hot-cathode gas or vaporfllled-type in which the cathode shall be protected "from damage thereto arising when an anode-cathode potential is applied prior to the to time that the cathode reaches a temperature at which its emission equals or exceeds the maximum anode current to be drawn through the discharge device.

Another object of my invention is to provide a system incorporating a hot cathode gas or 5 vapor-filled discharge device in which the cathode shall be protected from the deleterious effects of premature application of anode potential.

An incidental object of my invention is to provide a time delay relay system. 10

Another incidental object of my invention is to provide a time delay relay system in which the time of operation of the relay shall be variable with facility.

A further incidental object of my invention is to provide an illuminating unit of the glow discharge type that shall be capable of continuous operation over a long interval of time.

More concisely stated, it is an object of my invention to provide a circuit incorporating a hot-cathode gaseous electric discharge device provided with an element that shall be connected in the circuit in such manner as to completely protect the cathode from the deleterious effects arising from premature application of the anodecathode potential.

According to my invention, the discharge device is provided with a shield which completely encloses the cathode. The shield is so constructed that electrons from the cathode may be trans- 3o mitted through its surface. This object is accomplished either by providing the shield with one or more perforations or by constructing the shield of such thin material that it is punctured by the electrons from the emissive electrode as they move under the influence of the anodecathode potential. The interior surface of the shield is designed to be thermionically active. However, I have found that the shield, while it may be, need not be coated before it is mounted in the discharge device. An uncoated shield may be mounted adjacent to the cathode. After the cathode has operated for a short interval of time, suflicient coating material is projected from the cathode onto the shield to render the interior surface of the latter emissive.

The shield is connected in circuit with the cathode in such manner that when the cathode is below the proper temperature for emission, the shield operates as a blocking control electrode. 50 It is moreover disposed in such proximity to the cathode that it is heated thereby. As the temperature of the cathode rises, that of the shield also rises and a continuously increasing stream of electrons is emitted from the interior surface of 55 the shield. A continuously increasing current is therefore transmitted between the shield and the cathode. The efiect of this current is to so decrease the blocking potential of the shield that when the cathode is at the proper temperature for supplying current to the anode, the shield ceases to block the discharge between the cathode and the anode.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood irom the following description of specific embodiments when read in connection with the accompanying drawings, in which- Figure 1 isa view in section showing a discharge device constructed in accordance with my invention,

Fig. 2 is a view in section showing another discharge device constructed in accordance with my invention,

Fig. 3 is a view in section showing a glow discharge lamp constructed in accordance with my invention,

Fig. 4 is a diagrammatic view showing an embodiment of my invention,

Fig. 5 is a graph illustrating the operation of my invention, and

Fig. 6 is a diagrammatic view showing the elements of a time delay relay constructed in accordance with my invention.

The apparatus shown in Fig. 1 comprises an envelope I having a reentrant stem 3 and containing an atmosphere of gas or vapor. Through the rc-entrant portion 3 a plurality of metallic rods 5, and 9 are sealed. Two of the rods 5 and I serve as supports and as current conductors for a helical filament preferably composed of an alloy coated with a mixture of alkaline earth oxides. When the filament H is heated by current transmitted through the conductors, electrons are emitted thereby. An anode t3, composed of nickel, carbon or other suitable material, is sealed through the top of envelope The emissive electrode H is completely enclosed by a screening element |5 composed of a hollow cylinder H of wire mesh closed at the bottom by an insulating disk IS. The mesh cylinder I1 is secured to the disk l9, and the hollow assembly is supported on an insulating tube 2|, enclosing a portion of the conductor 5 that supports the emissive electrode H, and by the rod 9 which is welded to the mesh H. The: rod l9 serves also as a connector between the mesh l1 and the other elements of the. apparatus.

The mesh I1 is provided with a layer of emissive material on its interior surface either before it is mounted in the envelope or, from the emissive electrode, after it is mounted in the envelope. It is, moreover, disposed in such proximity to the emissive electrode II that when the latter is heated, the radiant energy emitted thereby raises the temperature of the mesh to a value at which electrons are emitted from its interior surface. When the mesh I! thus becomes emissive: it operates as a portion of the cathode. In addition, the emission therefrom tends to neutralize whatever blocking action it has as a control electrode and to permit the passage of current from the emissive electrode II to the anode |3 when the former attains the proper temperature.

The operation of my invention will be understood from a consideration of the apparatus shown in Fig. 4. In this system, an alternating difference of potential is impressed from a secondary-section 23 of a suitable transformer 25 between the anode 3 and the emissive electrode through the usual load 21. The emissive electrode l is heated from another secondary section 29 of the transformer 25. The screening element I5 is connected to the emissive electrode through a resistor 3| and a biasing battery 33. When the system is first energized by closing a switch 35 in the primary 31 of the transformer 25, heating energy is supplied to the emissive electrode I and a diiference of potential is impressed between the electrode II and the anode l3. If the emissive elctrode II and anode l3 were the only elements in the container I, positive ion bombardment of the electrode It would commence before it is heated to a safe temperature and the electrode would be seriously damaged.

In accordance with my invention the shield I5 is interposed between the emissive electrode II and the anode l3 and a negative potential is impressed thereon by the battery 33. The shield l5 thus operates as a control electrode to block the passage of substantial current between the emissive electrode H and anode l3 and protects the' electrode ll, As the temperature of the electrode I increases, it radiates more .and more energy to the shield, l5. The shield, in turn, being heated emits electrons which, in view of the fact that a positive potential is impressed between the electrode H and the shield ll, are collected by the electrode H and transmitted through the resistor 3|. A drop in potential of a polarity opposite to that of the biasing potential 33 is thus impressed across the resistor 3|, and this potential tends to compensate for the effect of the biasing potential. As the temperature of the shield increases, the blocking effect of the biasing potential decreases until a value is attained at which the shield no longer blocks the passage of current between the emissive electrode H and the anode l3. At this point the discharge device becomes fully operative and the shield l5 functions substantially as a portion of the cathode. The resistor 3| is so chosen that the blocking effect of the shield |5 persists until the emissive electrode H is at the proper temperature for passage of current.

In Fig. 5, the variation of the potential impressed between the shield I5 and the emissive electrode H as a function of time is illustrated graphically. Potential is plotted as ordinate and time as abscissa. The zero time coordinate corresponds to the instant at which heat is applied to the electrode The full line curves 39, 4|, 43, 45, 41, 49 and 5| correspond to different magnitudes of the resistor 3|, the curve 39 corresponding to a resistance of 1000 ohms and the curve 5| to a, resistance of 130 ohms. The point at which the discharge device becomes energized is represented by a discontinuity 53 in the slope. For the discharge device utilized in obtaining the data for the curves the shield ceases to have a blocking effect at approximately -8'volts.

As can be seen from a consideration of the full line curves 39, 4|, 43, 45, 41, 49 and 5| the interval of time during which the cathode is heated before a discharge is incited in the discharge device may be varied from approximately 20 seconds to approximately 75 seconds by varying the resistor 3| in series with the shield l5 from 1000 ohms to 130 ohms.

The broken line curve 55 shown in Fig. 5 illustrates the variation of the negative potential between the shield I5 and the emissive electrode II as the shield cools for the circuit corresponding to curve 39, i. e., for a 1000 ohm resistor. It is to be noted that for the particular tube utilized in providing the data for the curve, the shield becomes effective in blocking current between the anode I3 and theemissive electrode II approximately 5 seconds after the heating supply for the shield I 5 is turned ofi. This value may, of course, be varied by varying the structure of the discharge device and its appurtenant elements.

It is to be noted that in addition to operating as a protecting electrode for the cathode, the shield I5 may be utilized as an ordinary control electrode. In such a case, sufiicient biasing potential is provided in the shielding circuit to make certain that the control potential supplied does not energize the discharge device prematurely.

In Fig. 2, another discharge device, constructed in accordance with my invention, is shown. In this case, the filamentary electrode 51 is mounted on a ceramic tube 59, in turn supported on studs (not shown) projecting from disks 6| of ceramic or other insulating material. The ceramic disks 6| are, in turn, supported on rods 63 sealed through the re-entrant portion 3 of the envelope I. The rods 63 carry plates 65 that project through slots 61 in the disks GI and are welded to the filamentary portion 51 of the cathode. Each ceramic disk BI is provided with a steam portion 69 on which a cylinder 'II composed of perforated sheet metal is supported. The sheet metal cylinder II operates as a shield in the manner discussed above.

In Fig. 3, a lamp constructed in accordance with my invention is shown. The lamp comprises an envelope 73 through a reentrant portion I4 of which rods 15 project. A plurality of heating elements I! suitably supported on rods I5 are disposed within the envelope. Each filamentary element TI is enclosed within a tube I9 having disks 8| of ceramic or other insulating material at the ends and emissive walls 83 extending between the ends. The disks 8I are provided with shoulders 85 and 81 and the emissive walls 83 are supported between the innermost shoulders 8-5 of each set of disks. On intermediate shoulders 81 of the disks, screening members 89 are supported. The screening members 89 are preferably composed of perforated sheet cylinders similar to the cylinder utilized in a discharge device of the type shown in Fig. 2. Connectors 9| are welded to each of the perforated cylinders 89 and to the rods 15 to connect the screening member 89 and the emitting electrodes. Similar conductors 93 are welded to the emissive walls 83 and the rods 15. The filamentary elements I! are each welded to a short rod 95 at the top. The rods 95 project through the ceramic disks 8| and are welded to a cross piece 91. The cross piece 91 thus connects the emissive electrodes in series with each other. To support each of the assemblies I1, 19, 89 an upright member 99 sealed in the stem 14 and welded to the cross piece 91 at the center is provided. To provide the necessary vapor atmosphere, a globule of mercury IOI is disposed within the envelope.

Power is supplied to the lamp by connecting the cathodes to an alternating source. The source operates to heat the cathodes and at the same time to impress a difference of potential between them which causes current to pass a1- ternately in one direction and the other between the electrode assemblies.

It is to be noted that in the lamp a biasing potential is not provided between the shielding element 89 and the emissive electrode. I-have found that in the apparatus here involved biasing potential is not necessary since zero bias potential is suflicient to prevent the premature initiation as long as the pressure of the mercury vapor is low.

Incidentally, it is to be noted that in the apparatus of the type shown in Fig. 4, the biasing potential may sometimes be zero. Such a situation occurs in cases where the discharge device requires a positive control potential for ignition.

In Fig. '6, a time delay relay constructed in accordance with my invention is shown. The apparatus shown in this view to a large extent resembles the apparatus shown in Fig. 4. However, in lieu of a biasing battery 33, an alternating current bias is shown as utilized. It is obvious that these elements are interchangeable and their use depends in each case on the particular circumstances. This bias is supplied by a winding I83 of the secondary 25 which is so connected to the shielding element I5 that the po-- tential supplied is in opposite phase to the anodecathode potential. The biasing section I03 is connected to the shielding element I5 through a resistor I05 which may be selected at will from a set I01 of resistors.

When the switch in the primary 31 of the transformer 25 is closed, power is supplied to the discharge device. However, the discharge device does not become immediately operative. An interval of time elapses before a discharge is incited in the discharge device which depends on the magnitude of the resistor I05 selected and the biasingpotential applied. When a period of time corresponding to the particular resistor element l I15 connected passes after the switch 35 is closed, the discharge device becomes operative and energizes a relay I09 in its anode-cathode circuit.

The switch 35 and the relay I09 are used here only for the'purpose of illustration. The former symbolizes any operation which may take place to initiate the operation of the relay and the latter symbolizes any general work-circuit which may be supplied through the discharge device. In lieu of a set III! of resistors I05 a single variable resistor may moreover be utilized.

My invention has been shown and described herein as applied specifically to a hot cathode discharge device of the gas or vapor-filled type. On occasions, it may happen that the principles of my invention are applicable to hot cathode discharge devices of the high vacuum type. Where ,my invention is applied in a hot cathode high vacuum discharge device, such application is understood to fall within the scope of equivalents of my invention.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination an elctrode that is to be heated to emit electrons, means for heating said electrode, an electrode for collecting the electrons emitted by said first-named electrode, a member disposed adjacent to said emissive electrode in the path of the heating energy emitted by said emissive electrode, said member being capable of emitting electrons when it is heated from said first-mentioned electrode, means for impressing a diiierence of potential between said electron collecting electrode and saidemissive electrode, connecting means establishing a normal potential relationship between said member and said emissive electrode whereby when said member is below a predetermined temperature it operates as a blocking electrode to block the passage of current between said emissive electrode and said collecting electrode and when it is heated to a temperature above said predetermined value its blocking effect is suppressed and electrons pass between said emissive electrode and said collecting electrode. 7

2. In combination an electrode that is to be heated to emit electrons, means for heating said electrode, an electrode forcollecting the electrons I emitted by said first-named electrode, a member disposed adjacent to said emissive electrode to be heated by the heating energy emitted by said emissive electrode, said member being capable of emitting electrons when it is heated, means for impressing a difference of potential between said collecting electrode and'said emissive electrode, a current path including said member and said emitting electrode, said current path including means by the operation of which a difference of potential is impressed between said member and said emissive electrode of such magnitude that the transmission of current between said emissive electrode and said collecting electrode is blocked when the temperature of said member is below a predetermined value and additional means operating to vary the last-said difi erence of potential with the variation in temperature of said member in such manner that when said member is above a predetermined temperature passage of current between said emissive electrode and said collecting electrode is permitted.

3. Apparatus according to claim 2, characterized by the fact that the means included in said current path is a source of potential and an impedance, the polarity of the source of potential being such that said current path constitutes a circuit in which electrons emitted by said member are transmitted to said emissive electrode and through the source and impedance back to the member.

4. Apparatus according to claim 2, characterized by the fact that the means included in said current path is a source of potential and a resistor, the polarity of the source of potential being such that said current path constitutes a circuit in which electrons emitted by said member are transmitted to said emissive electrode and through the source and resistor back to the memher.

5. A time delay relay comprising an electrode that is to be heated to emit electrons, means for heating said electrode, another electrode, means for impressing a potential between said electrodes, 9. member disposed adjacent to said emitting electrode to be heated by the heating energy emitted thereby, said member being capable of emitting electrons when heated, a current path including said member and said emissive electrode through which the current emitted by said member is transmitted, said current path including means functioning to impress a potential between said member and said emissive electrode to block the passage of current between said emissive electrode and said other electrode when the temperature of said member is below a predetermined value, and a resistor through which the current from said member is transmitted to increase the potential of said member to such a. value that passage of current between said emissive electrode and said other electrode is permitted and means responsive to the current transmitted between said emissive electrode and said collecting electrode.

6. Apparatus according to claim 5, character ized by the fact that the resistor is variable and the time interval of the time delay may be set by adjusting the resistor to a predetermined value.

ERWIN F. LOWRY. 

